1. Field of the Invention
The present invention relates to a creasing apparatus that performs a creasing process on a sheet-like member (hereafter, referred to as a “sheet” in this specification) that has been conveyed from upstream before the sheets are bound together as a pile at the center section thereof and folded in two about the center section, and the present invention further relates to an image forming system that includes the creasing apparatus and an image forming apparatus, such as a copier, printer, facsimile, or digital multifunction peripheral that has the functions of a copier, printer, and facsimile in combination.
2. Description of the Related Art
Conventionally, a pile of sheets is obtained by combining sheets that are discharged from an image forming apparatus, the sheets in the pile are then bound together at the center section thereof, and the pile of center-bound sheets is folded in two at the center section, i.e., what is called center-folding or center-folded bookbinding is performed. If sheets in a pile are folded as a whole, the folded area of the outer sheet of the pile is stretched to a larger degree than that of the inner sheet. Because the formed image area on the folded area of the outer sheet is stretched, damage such as toner coming off may occur on the image area. The same phenomenon occurs in other folding processes such as Z-folding or letter-folding. The sheets in a pile may be folded in an insufficient manner because of the thickness of the pile.
A creasing apparatus called a creaser is already known. Before a folding process such as a process for folding a pile of sheets in two is performed, the creasing apparatus forms a crease in advance on an area of a sheet that is to be folded so that even the outer sheet can be easily folded, which prevents toner from coming off the sheet. In such a creasing apparatus, a crease is formed on a sheet in the direction perpendicular to the conveying direction by using a method, such as driving a roller and burning with a laser or pressing with a creasing blade.
When a processing function is performing a process, any processing function that is upstream of the processing function is stopped. Because the process on the upstream side cannot be started unless the process on the downstream side is completed, the processing efficiency is decreased. An apparatus that has a configuration to enable these processes to be performed in parallel is known (see Japanese Patent No. 4179012, Japanese Patent No. 3617936, and Japanese Patent No. 4355255). While the processing function on the downstream side is being executed, sheets that are processed using the processing function on the upstream side are in a stand-by state or being held back and, when the process using the processing function on the downstream side is completed, the sheets processed on the upstream side are conveyed downstream all together for processing.
A sheet conveying apparatus is disclosed in Japanese Patent No. 4179012 that includes a first path that conveys a sheet; a second path that conveys a sheet to a post-processing unit; a third path that discharges a sheet without any post-processing being performed; a switching unit that switches between the second conveying path and the third conveying path; and a fourth path that retains a sheet on the upstream side of the switching unit. A mechanism is also disclosed in Japanese Patent No. 4179012 in which a sheet conveyed by the second conveying path is retained by the fourth conveying path, and the sheet conveyed from the first conveying path is stacked together with the sheet conveyed along the second conveying path so as to be delivered downstream for post-processing.
A technology is disclosed in Japanese Patent No. 3617936 and Japanese Patent No. 4355255 in which a sheet is held back on the upstream side and, after the processing on the downstream side is finished, the held sheet is conveyed or the held sheet is stacked together with another sheet and is conveyed.
Because a creasing process requires a certain period of time, there is a productivity limitation. If the creasing process is performed by a pressing method, productivity conditions are particularly difficult. As described above, a technology is known in which, if there is a sheet to be processed on the downstream side, one or more sheets are held back on the upstream side. Although it is tried to hold back a sheet while a process is being performed by combining these technologies, because a process performed on the upstream side is a creasing process, they can't be just applied as they are.